How accurate is your Fitbit?

fitbitIt’s OK for steps, but not much else

I was feeling really good about myself the other day when I came home after finishing a 6,000 step walk that burned—according to the Fitbit Zip in my pocket—720 calories.


I boasted about this to my husband, who immediately burst my pride bubble by saying, “There is no way you burned that many calories in a 40-minute walk. Think about it.”

He was right. I knew in the back of my mind that 720 calories was just too high. Have you ever run on a treadmill for 15 minutes and felt beat down when the stupid machine displayed only 70 calories burned?

Later that same day I read about a new study that had tested several models of the most popular fitness trackers, Fitbit and Jawbone, and found them to be wildly inaccurate at measuring calories burned.

On average, the amount of energy exerted, or calories lost, was overestimated by 16 to 40 percent during ambulatory activities, such as walking, jogging and climbing stairs, and underestimated during household activities, including vacuuming, gardening and sweeping, by as much as 34 percent.

This new information is in addition to previous reports that Fitbit does not measure heart rate accurately, and doesn’t do a good job measuring the quality of your sleep.

But Fitbit does measure steps well.

The report did find that activities with a fairly well-defined motion, such as stair climbing or walking or jogging, counted the number of steps taken extremely well, within about 1 to 2 percent.

Save your money, just buy the Fitbit you need

I’ve posted many times that our health’s worst enemy might be our sedentary lifestyles. We need to be nudged and motivated and provoked to move. My Fitbit does that. I bought the cheapest model because I only wanted to track my steps, nothing else. (Although I now wish I had gotten the next model up, because the Zip has a coin battery that needs to be replaced, so that is not a cost savings.)

The Fitbit models that measure more also cost more—a lot more. Before you buy, give some thought to what you want or need from the device.

If I really needed to measure my heart rate, for health reasons, I certainly wouldn’t rely on a product that is not meant to be sold as a medical device. Worst case, as the current lawsuit against Fitbit contends, inaccurate readings could cause harm.

Related post: Don’t use the Instant Blood Pressure app

Consumer Reports did find two of the more expensive Fitbit models (the Surge and the Charge HR, which are also the two models under attack by the lawsuit) to be very accurate in measuring heart rate.

But I still wouldn’t trust my life to them. I’d use a watch and my own fingertips.


Frugal Nurse



How accurate is your Fitbit? — 2 Comments

  1. Ftbit bases the calorie burned rate on what your body burns just by living each day. I turned that feature off on mine. Also, I have the One, which I usually clip to my pants pocket. Sometimes, I wear it on my wrist if that works better with my outfit. I average 4000-5000 more steps each time I wear it on my wrist. So, arm movement counts, even when sitting.

    • Hi Ann, thanks for the comment. You bring up a good point that an activity tracker’s measurements can vary depending on where you wear it. That’s good to consider for more consistent data. In hindsight, I wish I had bought a One rather than a Zip; I don’t care about anything more than steps, but the Zip doesn’t charge via a USB and it doesn’t have as many wearing options. Oh, well. Cheers, FN